By Kaj Bjoerkman / IWAC AB
When Acoustic Research introduced their 'acoustic suspension woofer' it was a novelty to the Hi-Fi market. The idea was as simple as genious. Pre-designs of woofer elements relied to a great extent on the mechanical brake of the membrane using wrinkled outer edges. AR came up with the idea to make an airtight box and put a 'foam' instead of a wrinkled surrounding ring. The idea was to let the air in the box to brake the woofer-cone.
This idea produces 3 results:
Also: When the foam breaks the damage can lead to total disaster, if unnoticed or ignored. This is a worst case scenario and has to do with the voice coil. The voice coil is 'embedded' in a magnet. It moves up and down in this narrow space. If the foam breaks the voice coil is at danger to hit the mechanical structures within the magnet. This could lead to the destruction of the coil.
To further worsen the case, a broken foam on the AR-speaker is breaking the air-spring, the cone will loose most of it's breaking ability. It will start to move at uncontrolled amplitudes. Hopefully the listener will reckognize that something is amiss and stop further breakdown.
I had a 'rot' in my woofers 10 years ago. Then there was not so easy to find a cure other than to do it the 'Apple-upgrade-style'; pick the woofer up, open the window, throw it out and buy a new one!
Fortunately there are other ways to do this nowdays! You can refoam the speaker element at home yourselves. That's what this article is about!